Historically, most shoe soles typically have a homogenous hardness and are often made of a material with uniform properties throughout the sole. Soles that may be made of a rigid material may provide protection and support to a user's foot. However, a sole made of a rigid material may be uncomfortable in the areas of the sole that flex, such as the toe area, because the rigid sole may inhibit flexing.
On the other hand, a sole made of a soft material may provide comfort to the user's foot in addition to providing improved flexibility in the areas of the sole that are flexed. However, a sole made of a soft material may not provide sufficient support or protection to a user, which may lead to injuries or fatigue. Moreover, a soft material may not provide sufficient structural integrity to hold a predetermined shape over time, which in turn may lead to discomfort.
To alleviate the above problem, soles made of varying hardnesses may have been developed to provide both flexibility and support.
U.S. Publication No2003/0056397 to Hsiao appears to relate to a sole having a hard portion and a soft portion, where the hard and soft portions represent different hardnesses of the sole and where the hard portion seems to gradually change over to the soft portion and vice versa. The sole seems to eliminate a definite border, or separation, between the hard and soft portions.
U.S. Pat. No. 2,931,110 to Pietrocola appears to relate to a sole having two different materials, each being of a different hardness. A rigid material may be poured into a mold to form a majority of the sole, the rigid material may be a single unit having a plurality of holes. When cured, the rigid material is typically placed in a second mold where soft material may be poured into, and left to solidify within, the plurality of holes.
U.S. Pat. Nos. 4,899,467 and 4,658,516 to Mackey and Beck seem to relate to soles similar to the Pietrocola patent, where a majority of the sole is typically of a rigid material and where a soft material is normally placed in a selected area, such as the ball of the foot.
U.S. Pat. Nos. 5,025,573 and 4,348,003 to Giese and Beneteau seem to relate to soles having at least one layer of rigid material being fixed to at least one layer of soft material.
U.S. Pat. Nos. 4,020,569 and 6,571,491 to Fukuoka and Safdeye seem to relate to compounds for making a shoe sole, where the compounds are typically mixtures of rigid and soft materials.
U.S. Pat. No. 3,165,841 to Rollman seems to relate to a sole having a soft material making up a majority of the sole and a rigid material often located under a steel toe. Because the sole usually includes soft material over a majority of the sole, Rollman may lack sufficient support or structural integrity.
Although Pietrocola, Giese, Beneteau, Mackey, and Beck seek to provide soles with improved flexibility and adequate support for the shoes, the flexibility appears to be limited because the soles are substantially made of a rigid material. Pietrocola, Beck, and Mackey seem to show soles made of rigid materials having apertures in selected areas of the rigid materials and where soft materials are placed in the apertures. Giese and Beneteau seem to show soles having rigid materials substantially extend over the entire sole and where soft materials are attached to the rigid materials at particular locations. Although all of these references strive to improve flexibility over traditional shoes, the flexibility seems to be limited. Moreover, it appears that improving rigidity is at the detriment of flexibility, and vice versa.
What is desired, therefore, is a sole that overcomes the limited flexibility or limited rigidity problems associated with the prior art. What is also desired is a sole having improved flexibility without sacrificing support or structural integrity. A further desire is a sole having improved rigidity without negatively affecting flexibility.